Experimental Analysis of Ultra-High Strength NiTiHfPd Shape Memory Alloys

Ultra-high strength of NiTiHfPd alloys have been promising for specific application areas of SMAs. Thus, the main objective of this study is to further understand the high strength behavior of the alloys through experimental and theoretical studies. Shape memory response of an ultra-high strength Ni_45.3Ti_29.7Hf₂₀Pd₅ alloy was systematically investigated after aging at 550 °C for 5 h via constant-stress temperature cycling and constant-temperature stress cycling experiments. Shape memory behavior under a wide range of compressive stress levels from 300 to 1200 MPa was reported before and after stress cycling of 5000 times. The alloys showed a reversible strain of 1.3% against an ultra-high stress of 2 GPa. It is concluded that the combination of high strength and temperature capability mainly stems from high chemical complexity in addition to aging and will be quite advantageous in practical applications.